The commercials continue the chain's strategy of touting limited-time offers of specialty items along with a brand-building message. The first :30 features new Toaster sandwiches, Bacon Patty Melt and Chicken Patty Melt. In June, the chain touts two new shakes based on old-fashion pie flavors.

Provided initial results are strong, these spots will be followed by some two dozen more this year, said Kris Miotke, VP-sales and advertising.

GENESIS OF THE CAMPAIGN

The campaign stems from an advertising evaluation Sonic and its agency launched last fall, at a time of robust sales. Founded in 1953, the chain posted fiscal 1998 sales of more than $1 billion; same-store sales rose 8.1% for the six months ended in February.

While executives were open to a total ad overhaul, research revealed that wasn't needed. So the challenge became to improve upon existing work, said Scott Aylward, agency president.

"We're trying to get greater continuity in the look and sound," he said.

For instance, most ads previously featured a carhop, but not the same one. And a voice-over described the latest deal. Now the Katie character will do the selling and appear in most commercials.

The chain also had used various Beach Boys songs; now the new jingle will be used in all advertising.

Katie also will be used for in-store marketing materials.

LUXURY ASSIGNMENT

With Sonic, Mr. Aylward said, his agency has the luxury of creating work for a brand with unique points of difference from other hamburger chains. Its distinctive products include hot dogs called Extra-Long Cheese Coneys, Cherry Limeades and burgers made with fixings on the bottom bun.

"Sonic is not dependent upon the advertising to create the brand," Mr. Aylward said. "It is dependent on the advertising to show the brand. The deals we select show the proprietary nature of the menu. You'll never see us do a burger, a fry and a soft drink."

Ron Paul, president of restaurant consultancy Technomic, said the focus on points of difference makes sense.

"These kinds of chains have a heritage and a point of differentiation," he said. "If they tried to be real hip and with it and Generation Y, it would be a disconnect."

The new jingle may have some unfamiliar twangs. That's because two of the musicians are Sonic brass: CEO Cliff Hudson and Chief Operating Officer Ken Keymer.

"It's a nice little smile for all of us that our guys go the extra mile for our